Method of depositing metal-containing material onto an extended surface



United States Patent 3,147,154 METHOD OF DEPOSITING METAL-CONTAWING MATERIAL ONTO AN EXTENDED SURFACE Edward L. Cole, Glenliam, and Edwin C. Knowles, Poughkeepsie, N.Y., assignors to Texaco Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed May 25, 1961, Ser. No. 112,508 8 Claims. (Cl. 148-631) This invention relates in general to a method for depositing metal-containing material onto a supporting surface. In one of its more specific aspects, this invention relates to a method for plating or depositing a substantially continuous film or layer of metal or metal-containing material upon an extended surface or substrate from a solution containing a soluble salt of the metal. In another of its more specific aspects, this invention relates to a method for making a catalyst which comprises plating a metallic catalyst material on an extended surface from a solution containing a soluble metal salt or compound of the catalyst material.

It is well known in the art that elemental metal may be a precipitated in particulate or discrete powder form from a solution containing a soluble salt of the metal by the action of a reducing agent on the solution. This general concept is employed in the hydrometallurgical precipitation of elemental metal powder, particularly non-ferrous metals, where hydrogen is employed as the reducing agent. Reduction of the metal compound or salt and precipitation of the metal powder normally is carried out at elevated temperatures and at superatmospheric pressures. This method of producing metal powder is useful where a salt of the metal forms with ammonia a soluble complex ion which may be reduced with a suitable agent, e.g. hydrogen, to yield elemental metal. To facilitate precipitation of the metal in particulate form, the solution is generally stirred or otherwise agitated. More recently, it has been proposed to incorporate nucleating sites, for example, fine metal particles, in the solution of metal salt to further induce precipitation ofthe metal powder.

In accordance with the method of the present invention, elemental metal, or its intermediate product of reduction, is deposited from a solution of its salt by reduction as a substantially continuous film on an extended surface or substrate in contact with the solution, and not precipitated as discrete particles or powder as in the prior art. We found, quite unexpectedly, that when a suitable metal salt solution is pressured with hydrogen at an effective reduction temperature in a sub stantially quiescent state, the elemental metal is de-' posited, or plated, as a substantially continuous film on an extended surface or' substrate in contact with the solution, as explained more fully hereinbelow. The extended surface or substrate as employed herein, and in the appended claims, is defined as a surface or substrate of extended dimensions and is particularly of a length and geometric surface area substantially greater than that of discrete particles. As explained below, an extendedv surface having formed thereon a deposit of a metal in accordance with our invention is particularly suitable for use in a catalytic structure.

Accordingly, our invention involves broadly depositing a substantially continuous film of elemental metal, or its intermediate product of reduction, on an extended surface from a solution containing a soluble salt of the metal by the action of hydrogen on the solution'while maintaining the system in a substantially quiescent state. The invention is particularly applicable to those metals whose compounds or salts in solution form a soluble complex with a suitable stabilizing agent such as complexing agents which form soluble complex ions of the co-ordinate complex type, sequestering agents, chelating agents, dispersants and detergents. Salts of numerous metals form with ammonia, for example, a soluble complex ion of the coordinate type. The metal complex may be readily reduced to the elemental form, or its intermediate product of reduction, with a suitable reducing agent, described in greater detail hereinbelow. Metals from Groups I, VI and VIII of the Periodic Table of Elements, for example, copper, silver, gold, chromium, tungsten, molybdenum, iron, nickel, platinum,

- palladium and osmium are generally suitable for use in the present process. Other elemental metals, including many from Groups II, III, IV, V and VII of the Periodic Table, for example, zinc, aluminum, tin, zirconium, titanium, vanadium, tantalum and manganese can also be used.

The non-metallic ion or anion of the metal compound or salt to be precipitated from the ammoniacal solution may be of the more common inorganic or organic acids which form soluble salts of the metal. Also, the anion should not be reduced under precipitation conditions. Those anions usually employed include, sulfate, chloride, nitrate, carbonate and acetate. The solvent generally used is Water to form an aqueous solution of the metal complex, but suitable organic solvents for the metal salts, including alcohols, aldehydes, ethers, ketones, toluene and pyridine may be useful, as may liquid ammonia.

Although ammonia is the preferred stabilizing agent and the invention is described in greater detail in connection with solutions of this type, certain other stabilizing agents may be employed. Other suitable stabilizing agents include the organic primary, secondary and tertiary amines such as methyl amine, ethylenediamine and diethylenetriamine. In addition, stabilizing agents may include phosphates, especially pyrophosphate and metaphosphate, as well as citrate, acetate, oxalate, tartrate, o-phenanthroline, thiocyanate, thiosulfate, thiourea, pyridine, quinoline and cyano groups. Still further useful complex formations include the chloro, hydroxo and aquo complexes, such as the aquo-ammonia complexes. Olefin and olefin-like compounds are also useful, and may include, for example, ethylene, propylene, butadiene, etc., as well as the unsaturated cyclo compounds such as cyclohexene and styrene. However, the olefin and olefin-like compounds are desirably employed in a nonaqueous solvent, for example, benzene, toluene, pyridine, acetone and ether.

The concentration of the particular metal in solution will depend to a considerable extent upon the metal employed. Generally there appears to be no benefit from employing concentrations in excess of about 5 molar,

but the concentration of a metal in solution should be less than that at which a substantial amount will precipitate out in particulate form which may be deter-' rare or expensive elements, such as platinum, the con:

centration may advantageously be as low as 0.04 molar.

The element metal or its intermediate product of reduction is plated onto the extended surface from the solution.

with hydrogen in the presence of the extended surface. In the preferred embodiment of our invention, the extended surfaceis immersed or contacted with the solution containing a soluble compound of the metal, and the solution pressured with hydrogen atan effective reduction temperature, often at elevated temperatures and under superatmospheric pressures. The temperature and pressure employed in the reducing step depend to some extent upon the material undergoing reduction and may vary over a Wide range. Thus, for example, platinum may be deposited from ethylene chloroplatinate by reduction with hydrogen at room temperature and atmospheric pressure. However, with numerous other metals, reduction proceeds advantageously at elevated temperatures which may range up to about 500 F. and under a partial pressure of hydrogen of as high as 4,000 pounds per square inch or higher. Although higher temperatures and pressures may increase slightly the plating phenomenon, this increase generally is not practical.

It is essential during the plating operation of our invention to maintain the system under a relatively quiescent state, or maintain the system substantially free from turbulence. Agitating the dissolved metal salt solution or extended surface resulting in relatively violent or irregular motion should be avoided so as not to induce nucleation which would result in precipitation of the metal as discrete particles. In maintaining a relatively quiescent state during deposition, the metal is plated on the extended surface as a substantially continuous and adherent film.

Our invention is particularly suited for depositing or plating a substantially continuous film of elemental metal, or its intermediate product of reduction, which exhibits catalytic activity or which may be rendered active upon subsequent treatment on an extended surface or substrate for use in a catalytic structure. The substrate of the catalytic structure serves as the carrier or support member for the metal film deposited from a solution of its salt as explained above in detail. Where desired, the deposit is calcined and activated by subsequent treatment which includes, for example, oxidizing or sulfiding of the catalyst material. The deposit as the catalyst material thus employed in the catalytic structure is selected from the group consisting of metals, metal oxides and metal sulfides of Groups I through VIII of the Periodic Table, and more preferably of Groups I, VI and VIII, numerous examples of which have been set forth above.

The extended substrate employed in a catalytic structure formed in accordance with our invetion is not restricted to any particular configuration nor to any particular material. The substrate may be formed of a metal or non-metal suitable for use in a catalytic reactor and may include such materials as aluminum, steel, stainless steel or titanium, including sintered metal materials, or refractory materials including, for example, refractory metal oxides, e.g. alumina magnesia, silica, or refractory metal silicates or carbides. The configuration of the extended substrate may include bars, balls, chain, mesh, saddles, plates, sheet, tubes or the like, the members of the substrate not being less than about As-inch in its maximum dimension and more preferably A-inch, and of sufficient thickness to provide the required physical strength.

By way of example, elemental platinum useful as a reforming catalyst may be deposited on the substrate from an ammoniacal solution of a platinum salt, e.g. the chloride salt or chloroplatinic acid, by reducing the solution with hydrogen at elevated temperature and pressure as described above. Similarly, a silver deposit useful as a catalyst in the oxidation of ethylene may be formed on the substrate from an ammoniacal solution of silver sulfate. On the other hand, a deposit of nickel or of molybdenum similarly formed may be sulfided with hydrogen sulfide gas at elevated temperature, and the resulting sulfide catalyst then used in hydrogenation processes. A deposit of chromium may be oxidized for use as a catalyst in polymerization of olefins, or a deposit of iron may be oxidized for use in reaction of carbon monoxide with hydrogen to produce hydrocarbons.

A mixture of metal salts, all of which form complex ions with ammonia or other suitable stabilizing agents, may be used for forming a deposit of more than one catalytic element. By such means, a nickel-molybdenum catalyst or cobalt-molybdenum-nickel catalyst may be deposited on the substrate for use as hydrogenation catalysts. Also, nickel-molybdenum or nickel-tungsten salts may be complexed in a sodium citrate solution, and the metals precipitated from solution with hydrogen as described above. The co-deposits may then be calcined, sulfided, or otherwise activated Where desired.

During catalytic processing by conventional methods with solid particulate catalysts, the reactants are passed through a bed of porous catalyst particles, beads or pellets. In many such reactions employing organic materials at elevated temperatures, a carbonaceous deposit accumulates in the pores and openings of the catalyst as the process proceeds under continuous operating conditions. This deposition of carbonaceous material, commonly known as fouling of the catalyst, is a function of the reactants, the reaction products, the conditions of the process, and the catalyst, and certain types of reactions may be worse olfenders than others. Fouling may be particularly ex cessive when the reactants or products remain in contact With the catalyst for a relatively long time. When a porous catalyst is used, the reactants diffuse into the interior or central portion of the catalyst particles and may be retained for an excessive period of time whereupon decomposition of the reactants and products result in fouling the catalyst. Fouling results not only in a decrease in catalyst activity and loss in selectivity but also results in intensification of the heat transfer problem in the catalyst bed thereby resulting in local overheating or hot spots, particularly during regeneration of the catalyst.

It will be observed that the deposited film of metal as catalyst material formed on an extended substrate in accordance with our invention defines the depth of the catalyst layer, and therefore limits the extent of diffusion of the reactants through the pores or openings in the catalyst material to this shallow depth. As a consequence, substantially all of the active catalyst is exposed to the reactants, and excessive residence time, or entrapment, of the reactants is minimized or substantially eliminated. In this manner, we readily achieve with less catalyst material a reactive capacity equal to, or greater than, that accomplished by conventional catalysts.

The following examples will further illustrate our invention.

EXAMPLE I A solution of cupric ammonium sulfate was prepared by adding to 350 milliliters of distilled water, 47.5 grams of cupric sulfate, 22.5 grams of ammonium sulfate and 30 milliliters of ammonium hydroxide (28.7% by weight NH OH). The resulting solution was warmed on a hot plate and diluted by the addition of water to 500 milliliters. 35 milliliters of ammonium hydroxide was added, and the solution was boiled until the total volume of the solution measured 500 milliliters. The final solution was clear and had a pH of 9.

A stainless steel strip, measuring 1% by /2 by A was initially washed with acetone, then cleaned with 5% nitric acid solution and rinsed with water, dried and weighed. The strip was attached to the bottom end of an impeller in such a manner that the major plane of the strip lay horizontally. The impeller was rotatable by means of an electric motor. However, for the first run of this example the motor was not operated.

A 500 milliliter glass beaker containing 250 milliliters of the above solution was placed in an autoclave, and the stainless steel strip attached to the impeller was submerged in the solution such that the strip was covered with solution to a depth of about 4 inches. The impeller extended beyond the top surface of the autoclave, and was connected to the motor means. The autoclave was flushed with hydrogen and pressured with hydrogen to 265 p.s.i.g. at F. The autoclave was heated to 305 F. at which temperature the pressure of the reactor was 420 p.s.i.g. The reactor was held at 305 F. for /2 hour, then cooled to room temperature, vented and the stainless steel strip removed from the autoclave. The strip was dried at 750 F. for two hours. The stainless steel strip exhibited a heavy deposit of black material, and showed a net gain in weight of 0.1528 gram.

In a separate run to illustrate the advantages of our invention, the above procedure was repeated under agitation whereby only a relatively small amount of deposit resulted. Thus, the above procedure was repeated with the exception that during the hydrogen pressure step the motor was operated, and the impeller with the stainless steel strip attached thereto was rotated at 2,000 r.p.m. The strip had a stainless appearance and a net gain in weight of 0.0024 gram. It thus will be observed that employing the method of our invention rendered substantially superior results.

EXAMPLE II The method of Example I was repeated except that zirconium strips measuring approximately 2" by /2" by were employed. In the one instance Where the process was carried under a substantially quiescent condition, the zirconium strip, exhibiting a black deposit, had a net gain in weight of 0.0577 gram. On the other hand, when the solution was subject to agitation by reason of rotation of the impeller having the zirconium strip attached thereto, the strip had a net gain of only 0.0011

gram.

EXAMPLE III A plating solution was prepared by dissolving 112 grams of nickel sulfate hexahydrate, 73 grams of cobalt sulfate heptahydrate, 89 grams of ammonium molybdate tetrahydrate, and 100 grams of ammonium sulfate in 1500 milliliters of distilled water. The solution was warmed to 180 F., and 900 milliliters of ammonium hydroxide was added slowly. The resulting solution had a pH of 9.

A nickel strip measuring approximately 4" by by was washed first with acetone, then benzene, and water rinsed, then dried and weighed. The nickel strip was mounted vertically by means of a transite holder having a slot to hold the strip, and the transite holder was placed on the bottom of the 2000 milliliter beaker. A sufficient quantity of the above prepared solution was added to the beaker to completely submerge the nickel strip to a depth of about 4-inch. An impeller having a horizontal stirrer blade measuring about 1%" by /2" was inserted in the solution beside the nickel strip, the distance between the impeller and the strip being about 1% inches. The assembly was placed in an autoclave. The impeller was rotatable by electric motor means as in Example I, but the impeller was not rotated during this run. The autoclave was flushed with hydrogen and then pressurized with hydrogen at 260 p.s.i.g., at 75 F and heated to 300 F. A pressure of 500 p.s.i.g. was secured. The reactor was held at 300 F. for 2 hours, cooled and vented. The nickel strip, after being a calcined at 750 F., had a blue-gray color and showed a net gain in weight of 0.0396 gram.

The above procedure was repeated except the impeller was rotated at 2,000 r.p.m. during the hydrogen pressurizing step thereby agitating the solution. In this instance, the nickel strip actually showed a loss in weight of 0.0277 gram.

6 EXAMPLE v A copper vanadate solution was prepared by dissolving grams of potassium hydroxide in 350 milliliters of distilled water and adding thereto with stirring 70 grams of vanadium pentoxide. The solution was diluted to 1400 milliliters. 231 grams of citric acid was dissolved in 700 milliliters of water and then mixed with the basic solution of vanadium pentoxide. In another solution, 140 grams of copper sulfate pentahydrate was dissolved in 350 milliliters of water and 35 grams of nickel sulfate pentahydrate was dissolved therein. The latter solution was then thoroughly mixed with the other resulting solution having dissolved therein potassium hydroxide, vanadium pentoxide and citric acid. The final solution had a pH of 4.

In two separate runs, chrome steel pads prepared from metal mesh were employed as the base support. Each pad measured about 3%? along the sides and weighed approximately 20 grams. For both runs, 12 pads were stacked in a glass lined stainless steel tower having a length of 57" and an inside diameter of 1%". A sufiicient quantity of the copper vanadate solution was added to the tower to completely immerse the pads, the top pad being submerged to a depth of about A three foot void space remained at the top of the tower. The tower, in both runs, was flushed with hydrogen and pressured to 650 p.s.i.g. at room temperature. Hydrogen was introduced through an appropriate conduit at the bottom section of the tower and vented through a regulator at the top of the tower. The tower was then heated to 350 F. at which the pressure was 1000 p.s.i.g. The tower was held for five hours at 350 F. However, in Run No. 1, the rate of flow of hydrogen was 2 standard cubic feet per hour and in Run No. 2, 0.4 standard cubic foot per hour. After cooling and depressuring the pads were withdrawn from the tower, dried at 750 F. for two hours and weighed. The table below shows the net gain in weight of each pad, the pad represented by Sample No. 1 being the bottom pad and in the stack and Sample No. 12 being the top pad.

Table PLATING ON CHROME STEEL PADS Run No. 1 Run N o. 2

Pad Sample N o. Wt. gain, Pad Sample No. Wt. gain,

grams grams From the table it will be observed that those pads positioned near the top of the tower, and thereby farthest removed from the point of introduction of the hydrogen gas showed a greater gain in weight than the bottommost pad or pads. In addition, when the rate of flow of hydrogen was reduced in Run No. 2, there was a significant gain in weight for each pad. Consequently, a substantially greater amount of material was plated on those pads undergoing treatment in a relatively quiescent environment.

Having described our invention and certain embodiments thereof, we claim:

1. A method of depositing metal-containing material onto an extended support which comprises forming a solution of a soluble complex of metal of the metal-containing material to be deposited on said support, immersing said support in said solution and reducing said metalcontaining material from said solution by pressuring said solution with hydrogen and maintaining said solution at an effective reduction temperature while maintaining the system in a substantially quiescent state whereby said metal-containing material is deposited without nucleation on said support as a substantially continuous film.

2. A method according to claim 1 wherein the concentration of said metal in solution is not less than 0.01 molar.

3. A method according to claim 1 wherein said support is a metal.

4. A method according to claim 1 wherein said metal of said metal-containing material is formed as a soluble complex by complexing with an ammoniacal solution.

5. A method according to claim 1 wherein the concentration of said metal in solution is 0.5 to 2 molar.

6. A method according to claim 1 wherein said deposit of metal-containing material is activated for use as a catalyst by oxidizing said deposit to convert the metal to its corresponding oxide.

7. A method according to claim 1 wherein said deposit of metal-containing material is activated for use as a catalyst by sulfiding said deposit to convert the metal to its corresponding sulfide.

8. A method of depositing metal-containing materials as co-deposits of more than one metal onto an extended support which comprises forming a soluble complex of metals of the metal-containing materials to be deposited on said support in an ammoniacal solution, immersing said support in said solution, the concentration of each of said metals in solution being 0.01 to 5 molar, reducing said metal-containing materials from solution by pressuring said solution with hydrogen and maintaining said solution at an eifective reduction temperature while maintaining the system in a substantially quiescent state whereby said metal-containing materials are co-deposited without nucleation onto said substrate as a substantially continuous metal film.

References Cited in the file of this patent UNITED STATES PATENTS 1,880,741 Boswell Oct. 4, 1932 2,402,683 Signaigo June 25, 1946 2,734,821 Schaufelberger Feb. 14, 1956 2,740,708 Papee Apr. 3, 1956 2,767,083 Machiw Oct. 16, 1956 2,819,188 Metheny Jan. 7, 1958 2,827,400 Eisenberg et a1 Mar. 8, 1958 2,994,369 Carlin Aug. 1, 1961 2,994,577 Silverman Aug. 1, 1961 3,062,680 Meddings Nov. 6, 1962 

1. A METHOD OF DEPOSITING METAL-CONTAINING MATERIAL ONTO AN EXTENDED SUPPORT WHICH COMPRISES FORMING A SOLUTION OF A SOLUBLE COMPLES OF METAL OF THE METAL-CONTAINING MATERIAL TO BE DEPOSITED ON SAID SUPPORT, IMMERSING SAID SUPPORT IN SAID SOLUTION AND REDUCING SAID METALCONTAINING MATERIAL FROM SAID SOLUTION BY PRESSUREING SAID SOLUTION WITH HYDROGEN AND MAINTAINING SADI SOLUTION AT AN EFFECTIVE REDUCTION TEMPERATURE WHILE MAINTAINING THE SYSTEM IN A SUBSTANTIALLY QUIESCENT STATE WHEREBY SAID METAL-CONTAINING MATERIAL IS DEPOSITED WITHOUT NUCLEATION ON SAID SUPPORT AS A SUBSTANTIALLY CONTINUOUS FILM.
 7. A METHOD ACCORDING TO CLAIM 1 WHEREIN SAID DEPOSIT OF METAL-CONTAINING MATERIAL IS ACTIVATED FOR USE AS A CATAYLST BY SULFIDING SAID DEPOSIT TO CONVERT THE METAL TO IT CORRESPONDING SULFIDE. 